1. Field of the Invention
The present invention relates to lasers and particularly to a flashpumped, tunable, two-micron, solid state laser in which relaxation oscillations are suppressed.
2. Description of the Prior Art
Development of room temperature solid state lasers in the two-micron spectral range has received renewed attention recently because of potential applications in medicine and optical communications.
A pulsed, flashpumped, two-micron, solid state laser is ideally suited for medical applications because it can produce a high energy for a short period of time (e.g., 1 millisecond) for many laser/tissue interactions in various medical therapies.
An important consideration which determines the effectiveness of the pulsed, flashpumped, two-micron, solid state laser in medical applications concerns the absorption coefficient of the tissue specimen at the operating wavelength of the laser. It is well known that the absorption coefficient band of water, and therefore of tissue, is in the spectral region between about 1.9 microns and about 2.1 microns, with the peak absorption coefficient of water at about 1.96 microns. It is also well known that various tissues of the human body require different penetration depths into those tissues of the laser energy, and therefore different absorption coefficients, for laser ablation to correct for different medical problems associated with those tissues.
In certain surgical procedures, such as for laser operations on brain or eye tissue and the spine and for the tissue welding together of small blood vessels, a very high absorption coefficient is needed to obtain only a very small penetration depth of the laser energy into the tissue. In this case, laser pulses at a wavelength of about 1.95 or 1.96 microns would be utilized to obtain the very small penetration depth of the laser energy.
On the other hand, to obtain larger penetration depths of the laser energy, a lower absorption coefficient would be utilized. For example, in surgical procedures for the removal or treatment of a relatively large volume of tissue, such as a polyp, a tumor, hemorrhoids and cancerous tissue and for the tissue welding together of large blood vessels, a low absorption coefficient is needed to obtain a large penetration depth of the laser energy into the tissue. In such cases, laser pulses at a wavelength of about 2.0 or 2.1 microns would be utilized. In other words, the higher the desired penetration depth, the longer the wavelength (from the peak wavelength of about 1.95 microns) and therefore the lower the absorption coefficient.
As a consequence of the different wavelengths that are needed to obtain the different penetration depths for the different associated surgical therapies, a pulsed, flashpumped, two-micron, tunable, solid state laser is needed for these various medical applications. However, the use of such a pulsed, flashpumped, two-micron, tunable solid state laser in various medical applications presents two problems which bear on the effectiveness of that laser in such medical applications. First, the pulsed, flashpumped, two-micron, tunable, solid state laser must be able to produce a laser emission at any desired low or high gain transition over the exemplary wavelength range of from about 1.9 microns to about 2.1 microns in order to obtain the different penetration depths required for the different surgical therapies. Second, the typical transient spiking behavior of the pulsed, flashpumped, two-micron, solid state laser must be overcome in applications which require a spike-free laser output.